iotivity: deactivate it on uClibc

iotivity: deactivate it on uClibc

IoTivity makes use of std::sto* and this is deactivated because GCC
things uClibc does not support C11, but it supports this part, not C11
completely. To make IoTivity work with uClibc a patch for this bug is
needed:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58393

An option would be this patch:
https://github.com/maximeh/buildroot/blob/master/package/gcc/4.9.1/850-libstdcxx-uclibc-c99.patch

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>